How do you respond to a world in which everyone's a critic? San Francisco's Pizzeria Delfina is having at laugh at their Yelp users' expense by printing their worst one-star complaints onto staff t-shirts.
How direct do the quotes get? One simply states, "This place sucks."
I've found that Yelp (and similar sites) have been a pretty reliable means of finding good food in an unfamiliar city. But just like letters to the editor, it's usually the most upset or ecstatic people who will find the need to vent publicly about the experience.